This invention relates generally to methods for checking for faultily plated-through bores in printed circuit boards and, in particular, to a method for checking for faultily plated-through bores by means of a light transmitter on one side of the respective bore and a receiver on the other side, which receives light penetrating through voids of the plated-through bore.
In order to check printed circuit boards for faultily plated-through bores, typically specimens are removed from a group of printed circuit boards and are laterally ground until half of the bores are removed. At the other side, the board is ground off up to about 1 mm from the hole walls. Utilizing a light source, light is then directed onto the bore at this opposite side and the potential light penetration is observed on the opposite side, thus, indicating occurring pores or voids in the metallization.
In this method, however, the printed circuit board to be tested must be destroyed and the preparation of the specimen takes considerable time.
European patent application No. 111 404 discloses the use of a light transmitter arranged at one side of the bore and the light receiver arranged at the other side. The bore to be tested is covered at the light transmitter side, and only light passing through potential pores or voids in the plate-throughs is then received by means of a light receiver.
This testing method, however, is not suitable for multi-layer printed circuit boards or structured printed circuit boards, since the respective metal layer would hinder the light passage. Moreover, this testing method can only be carried out after the conclusion of the manufacturing process.